Stress-induced reinstatement of amphetamine-conditioned place preference and changes in tyrosine hydroxylase in the nucleus accumbens in adolescent rats

Unlocking the role of dorsal hippocampal α4β2 nicotinic acetylcholine receptors in Ethanol-Induced conditioned place preference in mice

Alcohol Use Disorder (AUD) presents a significant and challenging public health concern, marked by a dearth of effective pharmacological treatments. Understanding the neurobiological underpinnings of AUD is of paramount importance for the development of efficacious interventions. The process of addiction entails the acquisition of associative behaviors, prominently engaging the dorsal region of the hippocampus for encoding these associative memories. Nicotinic receptor systems have been implicated in mediating the rewarding effects of ethanol, as well as memory and learning processes. In our current investigation, we delved into the role of α4β2 nicotinic acetylcholine receptors (nAChRs) within the dorsal hippocampus in the context of ethanol-induced conditioned place preference (CPP), a robust model for scrutinizing the rewarding properties and drug-associated behaviors. To establish CPP, ethanol (2 g/kg) was administered intraperitoneally during a 8-day conditioning phase. Fos immunohistochemistry was employed to assess the involvement of discrete subregions within the dorsal hippocampus in ethanol-induced CPP. Additionally, we probed the influence of α4β2 nAChRs on CPP via microinjections of a selective nAChR antagonist, dihydro-β-erythroidine (DHBE, at dosages of 6, 12, and 18 µg/0.5 µL per hemisphere) within the hippocampus. Our results unveiled that ethanol-induced CPP was associated with an increase Fos -positive cells in various subregions of the dorsal hippocampus, including CA1, CA2, CA3, and the dentate gyrus. Intrahippocampal administration of DHBE (at doses of 6 and 18 µg/0.50 µL per hemisphere) effectively blocked ethanol-induced CPP, while leaving locomotor activity unaffected. These findings underscore the critical involvement of the dorsal hippocampus and α4β2 nAChRs in the acquisition of ethanol-associated learning and reward.

Effects of biperiden (cholinergic muscarinic m1/m4 receptor antagonist) on ethanol conditioned place preference in mice

BACKGROUND

Previous studies suggest that muscarinic cholinergic receptors might act upon the dopamine release in the mesolimbic system and alter drug-reinforcing values related to drug craving.

AIMS

We examined the effects of systemic biperiden administration, a muscarinic cholinergic (M1/M4) receptor antagonist, on ethanol (dose of 2 g/Kg) conditioned place preference (CPP), neuronal activation, dopamine and its metabolites levels in the nucleus accumbens.

METHODS

Thirty minutes before the ethanol-induced CPP test, mice received saline or biperiden at doses of 1.0, 5.0, or 10.0 mg/kg. The time spent in each compartment was recorded for 15 min. After the CPP protocol, animals were euthanized, and we investigated the activation of the nucleus accumbens by immunohistochemistry for Fos. We also quantified dopamine, homovanillic acid (HVA), and dihydroxyphenylacetic acid (DOPAC) levels in the nucleus accumbens by high-performance liquid chromatography (HPLC). Additionally, the rotarod was employed to evaluate the effects of biperiden on motor coordination.

RESULTS

Biperiden at different doses (1.0, 5.0, and 10.0 mg/kg) blocked the expression of ethanol-induced CPP. These biperiden doses increased the number of Fos-positive cells and the dopamine turnover in the nucleus accumbens. None of the doses affected the motor coordination evaluated by the rotarod.

CONCLUSIONS

Our results show that biperiden can modulate the effect of alcohol reward, and its mechanism of action may involve a change in dopamine and cholinergic mesolimbic neurotransmission.

Effects of environmental enrichment on reinstatement of methamphetamine-induced conditioned place preference

OBJECTIVE

The influence of environmental enrichment (EE) on reinstatement to methamphetamine (METH) seeking in rat model was investigated.

METHODS

Wistar rats were divided to receive saline (1 ml/kg) or METH (1 mg/kg, i.p.) for 8 days during the conditioning training in the conditioned place preference (CPP) paradigm, which is one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. Rats were then kept in either isolated (IE) or enriched environment (EE) for 30 days during the extinction training. Animals were finally examined for reinstatement provoked by i.p. injections of METH.

RESULTS

Saline injections during the conditioning phase did not change CPP during reinstatement in animals of IE or EE control groups. METH injections reinstated place preference in the IE animal group. Interestingly, EE significantly blocked this reinstatement effects of METH.

CONCLUSION

These results show the important role of social interactions and positive environment conditions in preventing reinstatement to drug use.

Repeated restraint stress potentiates methylphenidate and modafinil-induced behavioral sensitization in rats

Stress increases the susceptibility of drug abuse and drugs of abuse impair behavioral tolerance. It has been shown that stress exposure enhances the sensitivity to the reinforcing properties of drugs, augments locomotor sensitization effects of drugs of abuse and impairs behavioral tolerance. Previously, it has been shown that long-term administration of psychostimulants (Methylphenidate and Modafinil) induced locomotor sensitization effect that was more pronounced after 13 days of drug administration and was greater at high dose. The present study is designed to investigate the relationship between restraint stress and psychostimulants (Methylphenidate and Modafinil) that induced sensitization. Methylphenidate (10 mg/kg/day twice a day), modafinil (75 mg/kg/day once daily), and saline (0.9% NaCl; 1 ml/kg/day) were administered orally to treated and control animals. Rats were exposed to immobilization stress for 30 days (until locomotor sensitization produced) to monitor any change in drug-induced behavioral sensitization. The motor activity was compared daily by using familiar environment of home cage and weekly by novel environment of open field. The results show that the methylphenidate and modafinil-induced locomotor sensitization is enhanced and impaired behavioral tolerance in repeated restrained rats. It shows that the psychostimulants like methylphenidate and modafinil produce greater locomotor sensitization in stressful environment, suggesting addictive effects of stress and psychostimulants (methylphenidate/modafinil) on dopaminergic neurotransmission. These finding may be helpful to develop potential pharmacotherapies for the patients with co-occurring depression and substance abuse/dependence disorder.

Role of the orexin receptors within the nucleus accumbens in the drug priming-induced reinstatement of morphine seeking in the food deprived rats

Orexin plays a key role in mediating stress-induced drug relapse. However, the role of different types of orexinergic receptors that modulate stress-induced drug seeking remains unknown. The nucleus accumbens (NAc) has an important role in the reward system and receives orexinergic projections of the lateral hypothalamus. In addition, orexin interacts with other receptors that are involved in drug reinstatement. Therefore, in the present study, the role of orexin receptors in the NAc in morphine priming- induced reinstatement and the effect of food deprivation (FD) on drug reinstatement were examined. The extinguished morphine preference rats were tested for reinstatement following the 24-h FD condition after conditioning was induced. In the other groups, the animals were given intra-accumbal administration of SB334867 (01, 1 and 10 nM/0.5 μl DMSO) as an orexin-1 receptor antagonist and TCSOX229 (1, 5 and 25 nM/0.5 μl DMSO), as an orexin-2 receptor antagonist. The results showed that the blockade of two types of orexin receptors in the NAc remarkably attenuated the effect of FD on the drug reinstatement; however, they were more effective in FD condition. These findings indicate that the NAc is a brain area within which orexin has a fundamental role in the effect of stress on morphine-induced reinstatement and the effect of food deprivation- on the reinstatement of morphine.

Inhibiting effects of rhynchophylline on methamphetamine-dependent zebrafish are related with the expression of tyrosine hydroxylase (TH)

In this study, to study the effect of rhynchophylline on TH in midbrain of methamphetamine-induced conditioned place preference (CPP) adult zebrafish, place preference adult zebrafish models were established by methamphetamine (40μg/g) and the expression of TH was observed by immunohistochemistry technique and Western blot. Ketamine (150μg/g), high dose of rhynchophylline (100μg/g) group can significantly reduce the place preference; immunohistochemistry results showed that the number of TH-positive neurons in midbrain was increased in the methamphetamine model group, whereas less TH-positive neurons were found in the ketamine group and high dosage rhynchophylline group. Western blot results showed that the expression of TH protein was significantly increased in the model group, whereas less expression was found in the ketamine group, high dosage rhynchophylline group. Our data pointed out that TH plays an important role in the formation of methamphetamine-induced place preference in adult zebrafish. Rhynchophylline reversed the expression of TH in the midbrain demonstrates the potential effect of mediates methamphetamine induced rewarding effect.

Stress-Induced Locomotor Sensitization to Amphetamine in Adult, but not in Adolescent Rats, Is Associated with Increased Expression of ΔFosB in the Nucleus Accumbens

While clinical and pre-clinical evidence suggests that adolescence is a risk period for the development of addiction, the underlying neural mechanisms are largely unknown. Stress during adolescence has a huge influence on drug addiction. However, little is known about the mechanisms related to the interaction among stress, adolescence and addiction. Studies point to ΔFosB as a possible target for this phenomenon. In the present study, adolescent and adult rats (postnatal day 28 and 60, respectively) were restrained for 2 h once a day for 7 days. Three days after their last exposure to stress, the animals were challenged with saline or amphetamine (1.0 mg/kg i.p.) and amphetamine-induced locomotion was recorded. Immediately after the behavioral tests, rats were decapitated and the nucleus accumbens was dissected to measure ΔFosB protein levels. We found that repeated restraint stress increased amphetamine-induced locomotion in both the adult and adolescent rats. Furthermore, in adult rats, stress-induced locomotor sensitization was associated with increased expression of ΔFosB in the nucleus accumbens. Our data suggest that ΔFosB may be involved in some of the neuronal plasticity changes associated with stress induced-cross sensitization with amphetamine in adult rats.

Stress induces behavioral sensitization, increases nicotine-seeking behavior and leads to a decrease of CREB in the nucleus accumbens

Experimental evidence shows that exposure to stress engenders behavioral sensitization and increases drug-seeking and leads to intense drug taking. However the molecular mechanisms involved in these processes is not well known yet. The present experiments examined the effects of exposure to variable stress on nicotine-induced locomotor activation, cAMP-response element-binding protein (CREB) and extracellular signal-regulated kinase (ERK) activity and nicotine intravenous self-administration in rats. Male Wistar rats were exposed to variable stress that consisted of the exposure to different stressors twice a day in random order for 10 days. During this period the control group was left undisturbed except for cage cleaning. Ten days after the last stress episode, rats were challenged with either saline or nicotine (0.4 mg/kgs.c.) and the locomotor activity was recorded for 20 min. Immediately after behavioral recordings rats were sacrificed and their brains were removed to posterior western blotting analysis of CREB, phosphoCREB, ERK and phosphoERK in the nucleus accumbens. An independent set of control and stressed animals were subjected to an intravenous nicotine self-administration protocol. The break point during a progressive ratio schedule and nicotine intake patterns during a 24-hour binge was analyzed. Repeated variable stress caused a sensitized motor response to a single challenge of nicotine and decreased CREB in the nucleus accumbens. Furthermore, in the self-administration experiments previous stress exposure caused an increase in the break point and nicotine intake.

Behavioral effects of chronic adolescent stress are sustained and sexually dimorphic

Evidence suggests that women are more susceptible to stress-related disorders than men. Animal studies demonstrate a similar female sensitivity to stress and have been used to examine the underlying neurobiology of sex-specific effects of stress. Although our understanding of the sex-specific effects of chronic adolescent stress has grown in recent years, few studies have reported the effects of adolescent stress on depressive-like behavior. The purpose of this study was to determine if a chronic mixed modality stressor (consisting of isolation, restraint, and social defeat) during adolescence (PND 37-49) resulted in differential and sustained changes in depressive-like behavior in male and female Wistar rats. Female rats exposed to chronic adolescent stress displayed decreased sucrose consumption, hyperactivity in the elevated plus maze, decreased activity in the forced swim test, and a blunted corticosterone response to an acute forced swim stress compared to controls during both adolescence (PND 48-57) and adulthood (PND 96-104). Male rats exposed to chronic adolescent stress did not manifest significant behavioral changes at either the end of adolescence or in adulthood. These data support the proposition that adolescence may be a stress sensitive period for females and exposure to stress during adolescence results in behavioral effects that persist in females. Studies investigating the sex-specific effects of chronic adolescent stress may lead to a better understanding of the sexually dimorphic incidence of depressive and anxiety disorders in humans and ultimately improve prevention and treatment strategies.